Efficiency of combined process of ozone and bio-filtration in the treatment of secondary effluent Smriti Tripathi b,⇑ , B.D. Tripathi a,⇑ a Centre for Environmental Science and Technology, Banaras Hindu University, Varanasi 221005, India b Pollution Ecology Research Laboratory, CAS Botany, Banaras Hindu University, Varanasi 221005, India article info Article history: Received 19 February 2011 Received in revised form 11 April 2011 Accepted 12 April 2011 Available online 20 April 2011 Keywords: Biofiltration Ozonation Wastewater treatment Macrophytes Heavy metal toxicity abstract The present work was aimed at studying the efficiency of the combined process of biofiltration with ozonation to improve the quality of secondary effluent. The secondary effluent from the Dinapur Sewage Treatment Plant Varanasi, India was used in this work. The process of biofiltration with the plant species of Eichornia crassipes and Lemna minor, at a flow rate of 262 ml min À1 and plant density of 30 mg L À1 for 48 h, in combination with the process of ozonation with ozone dose of 10 mg L À1 and contact time of 5 min was applied. Results revealed that combined process was statistically most suitable for the highest degradation of physico-chemical and microbial parameters with improving BDOC value. The biofiltration process is able to remove highest percentage of toxic heavy metals from the secondary effluent without production of toxicity. This technique is highly recommendable for tropical wastewater where sewage is mixed with industrial effluents. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction India has emerged as a fast developing nation resulting in rapid industrialization and urbanization. This has imposed a serious threat of water pollution manifold. It is estimated that 22,900 mil- lion liters per day (MLD) of domestic wastewater and 13,500 MLD of industrial wastewater is generated from cities in India. The treatment capacity available for domestic wastewater is only for 5900 MLD and for industrial wastewater is only 8000 MLD. Urban sewage contains many toxic organic and inorganic substances which are not properly removed in the traditional Sewage Treat- ment Plants (Chen et al., 2005). Therefore, removal of these toxic substances and metals from primary and secondary treated sewage has drawn the attention of many workers (Weis and Weis, 2004; Brix and Arias, 2005). Analytical results revealed that wastewater effluent from these traditional treatment plants contains readily biodegradable organic matter, inorganic and organic chemicals, anaerobic and aerobic biological systems and toxic heavy metals, i.e., Cr, Cd, Cu, Zn, Fe and Ni. Secondary treated wastewater is dis- charged to the Ganga River that serves the populations of northern India. This inadequate disposal of waste water has created pollu- tion problems (Dyer et al., 2003). The conventional and advanced treatment processes (i.e. micro- filtration (MF) or ultra-filtration (UF) technology) are well-known but due to their large land occupation, complicated operation, sophisticated management and its possible higher cost they can’t be widely used (Bao et al., 2005; Wang et al., 2008). Growing con- cerns about the environment have resulted in the development of new environment friendly and cost effective technologies to mini- mize the problem of wastewater. Natural aquatic systems have created substantial interest with regards to their potential use for wastewater treatment and re- source recovery, using green environments. Biofiltration is one of the ways to solve the problem of water pollution (Soltan and Rashed, 2003). Various aquatic macrophytes have been tested as biofilters to purify water by removing nitrogen and phosphorus, elements that cause eutrophication (Upadhyay et al., 2007). Aqua- tic macrophytes have great potential to accumulate heavy metals inside their plant body (Mishra and Tripathi, 2009). Aquatic macro- phytes can also remove sulphadimethoxine (drug) (Forni et al., 2001) and metals like Sr, Cu, Cd, Zn, Cr, Fe, Ni, Pb, Au, Pt, and even radioactive elements such as U (Maine et al., 2006; Mishra and Tripathi, 2009). This system requires low capital and offer compet- itive operating cost and also to operate and maintain. Relatively few studies have been reported on the use of floating plants for wastewater treatment with circulation and aeration (Kadlec and Knight, 1996; Boyd, 1998; Turrel and Leeds-Harrison, 2004). Water circulation prevents thermal and chemical stratification. Water cir- culation generates flow across the pond bottom and helps maintain oxygenated conditions at the mud water interface (Boyd, 1998). Circulation of water seems to stimulate phytoplankton growth (Sanares et al., 1986), with possible increase in production of 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.04.035 ⇑ Corresponding author. Tel.: +91 0542 2311130; fax: +91 2368174. E-mail addresses: smrititripathibhu@gmail.com, smriti_envs@yahoo.co.in (S. Tripathi), tripathibd1947@gmail.com (B.D. Tripathi). Bioresource Technology 102 (2011) 6850–6856 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech